This invention relates in general to a method of growing single crystals of neodymium pentaphosphate and in particular to such a method in which the resulting single crystals are greater than one centimeter in size and of high purity and quality.
The requirement for low-threshold high-efficiency laser sources for miniaturized rangefinder and fiber optic communication applications has led to the study of rare earth pentaphosphate compounds. Neodymium pentaphosphate (NdPP) has recently emerged as a promising 1.05.mu.m laser material operating in pulsed and continuous wave modes, with thresholds of the latter reported less than one milliwatt. In contrast to doped lasers such as Nd:YAG, NdPP is a stoichiometric compound (NdP.sub.5 O.sub.14) which accommodates up to thirty times more Nd than YAG.
Heretofore, NdPP has been prepared by a method generally involving addition of the rare earth oxide and diluent oxide (if wanted) to a crucible containing orthophosphoric acid at approximately 200.degree. C. After the oxides are added, the crucible is covered and placed in a resistance furnace at temperatures to 600.degree. C. After a period ranging from one to two weeks, the furnace is cooled and the crystals are extracted from the crucible by leaching the remaining polyphosphoric acid with hot water. This process has typically yielded hundreds of small crystals ranging from one to several millimeters in length. Because of their limited size and quality, these crystals cannot be used as NdPP lasers in certain prototype components such as rangefinders and target designators using transverse and longitudinal optical pumping.